The central theme of our research is the nature of host- specificity. Because the majority of the arthropod-borne diseases of man are zoonoses, the primary vectors of such diseases to man are necessarily arthropods with relatively little host-specificity and, therefore, with broad host spectra which include man. Highly host- specific arthropod vectors are extremely important in the ecology of zoonotic diseases, but they are involved in the maintenance of the disease in its non-human host populations. To understand the relative lack of host-specificity in the vectors of zoonoses to man, one must first understand the determinants of host-specificity. Our research objectives are to elucidate the behavioral, physiological, immunological and ecological factors that influence or determine the host spectra of parasitic mites and ticks, the ways in which these factors regulate populations of these organisms, and the effects of such factors on the epizootologies and epidemiologies of acarine-transmitted diseases. We are conducting comparative studies of mites and ticks with narrow and broad host spectra to determine the sensory behavior patterns involved in host-selection and feeding. These investigations include analyses of environmental stimuli, host immune mechanisms and physiological factors, such as nutritional state, age, water balance and circadian rhythms, which modify behavior and interact to influence host-preference or host-specificity. The primary subjects of these studies have been a highly host-specific campestrine parasite, the rabbit tick (Haemphysalis leporispalustris), and the purple martin mite (Dermanyssus prognephilus), a nidicole that appears to be more habitat-specific on the nesting site of its host than host-specific on the bird itself. We propose to continue to study these acarines and to compare these with another rabbit-specific tick, Ixodes dentatus; a tick with a broad host spectrum, such as Dermacentor andersoni or variabialis; and some other nidicolous laelapoid mites.